Bikes like these don't do anything I can't do on my Rivs, so it isn't exactly revolutionary. The disk brakes are cool though.
There's something to your comment in that gravel race bikes are in someways a throw back to more traditional bikes that allowed the use of wider tires, before everybody started buying road bikes that are essentially road racing bikes.
That said, I doubt you'd finish Dirty Kanza on a Rivendal Roadeo due to the 33mm tire limit, and the lack of mud clearance from the caliper brakes.
The DK promoters recommend tires at least 2" wide. The ability to take really wide tires is what differentiates gravel grinders.